The larynx serves multiple functions, including control of respiration, airway protection, coordination of swallowing, and phonation. During swallowing, the larynx closes the airway in order to prevent aspiration of food or liquid. During inhalation, the larynx must not occlude the airway, and during speech, it must be positioned in order to accomplish phonation. Moreover, speech requires extremely precise movements of the larynx.
Spasmodic dysphonia (SD) is a focal, action-specific dystonia of the laryngeal musculature during phonation. It has a profound effect on patients' productivity and quality of life. The standard treatment for SD is botulinum toxin (BTX) injection of the laryngeal musculature. Unwanted side effects of adductor muscle injections include the loss of phonatory volume, breathiness, and dysphagia; whereas those of abductor muscle injections include dyspnea due to airway compromise.
The injections are painful and must be repeated nearly every 3 months. Due to the delayed onset of BTX effects and increasing symptoms prior to repeat injection, optimal voicing is achieved during only 30% of the injection cycle.